The heart failure caused by myocardium infarction and other factors (toxic substance, drugs, alcohol, genetic variation, gene mutation, virus or bacterial infection) is a major reason for death. According to statistics, the deaths caused by chronic heart failure and myocardium infarction account for more than 50% of total deaths caused by cardiovascular diseases. Additionally, the population suffered from the heart failure and myocardium infarction become younger, which has attracted a lot of attention from medical field.
The thrombosis of coronary artery, or genetic variations or mutation of pertinent genes, or the effect of toxic substance, drugs, alcohol, virus or bacterial infection can cause the death of some of the cardiomyocytes, which cannot regenerate, causing the irreversible injury of myocardium. Then the ventricle gets remodeled, leading to the thinning of ventricular wall, accompanied by the proliferation of fibroblasts and formation of scar tissue. Consequently, the functionality of myocardium decreased gradually, leading to the heart failure eventually. Recent studies showed that the remodeling of the ventricle could be inhibited by patching a soft material to strengthen the ventricular wall and prevent the proliferation of fibroblasts and formation of fibrosis tissue, improving the functionality of myocardium. Possible mechanisms include, (1) improving local mechanical microenvironment of myocardium, inhibiting fibroblast proliferation, promoting myocardial regeneration and angiogenesis; (2) increasing wall thickness, reducing ventricular wall pressure, stabilizing ventricular size, remodeling ventricular geometry, and preventing ventricular aneurysm formation.
The early studies used devices to wrap both of the ventricles, such as the Acorn CorCap and Paracor HeartNet ventricle support device. Then the left ventricle support devices, such as Myocor Coapsys and CardioClasp, were developed. The implantation procedures of the above devices are very complicated. Additionally, the size of these devices is too large that will cause harmful influence on the normal myocardium through contacting effect. In the recent years, researchers developed strengthening materials which was locally implanted to the myocardium that suffered from myocardial infarction. For example, Fujimoto et al sutured a PEUU film on the myocardium of rat heart with acute infarction (Ref. An Elastic, Biodegradable Cardiac Patch Induces Contractile Smooth Muscle and Improves Cardiac Remodeling and Function in Subacute Myocardial Infarction, 2007). Liao et al sutured a commercial double-layered film on the surface of ventricle with chronic infarction (Ref. Attenuation of Left Ventricular Adverse Remodeling with Epicardial Patching after Myocardial Infarction, 2010). Chi et al glued chitosan-hyaluronan/silk fibroin patches on the surface of ventricle of rat with chronic myocardial infarction (Ref. Cardiac Repair Using Chitosan-hyaluronan/silk Fibroin Patches in A Rat Heart Model with Myocardial Infarction, 2013).
The studies all reported positive results, proving the evidence of treating myocardial infarction by strengthening the myocardium with biomaterials. However, some limitations exist for the present materials. Firstly, the biomaterials used so far are not sticky and must be sutured on the surface of ventricle, which on one hand leads to the complexity of surgery, increasing the risk and causing injuries to the myocardium and on the other hand causes the local stress concentration on the myocardium. Secondly, the myocardium is characterized by fast relaxation and relatively slow creep. While different from myocardium, the present biomaterials are mostly elastic and this mismatch in mechanical property will induce the disorder of heartbeat. Thirdly, most of the present materials are not degradable in vivo nor degrade fast enough, which leads to the foreign body reaction from the host tissue. Lastly, the present patching materials are not injectable and need to be implanted though open-chest surgery, which is a complicated surgery with high risk.